Fear-related disorders such as Post-Traumatic Stress Disorder (PTSD) are often characterized by an inability to inhibit and extinguish fear memories leading to pathological expression of fear-related behaviors. For progress to occur with targeted rationally-designed therapeutic approaches, a greater understanding of the neural circuitry mediating fear inhibition and extinction is needed. This proposal utilizes cutting-edge, cell- type specific approaches targeting the amygdala to align with NIMH research priorities by cutting across many of the RDoC in the NIH strategic plan for identifying the pathophysiology of fear-related disorders. It is critical that we understand the role of specific cell types within the amygdala supporting fear inhibition and fear extinction learning. It is known that the Basolateral Amygdala (BLA) modulates fear expression via projections to the medial (CeM) and lateral division (CeL) of the central amygdala, in part through modulation via the Intercalated Cell Nuclei of the Amygdala (ITC), which receive inputs from medial prefrontal cortex (mPFC) and act as an inhibitory gate to the CeL. We will target the Thy1, FoxP2, and PKC??subpopulations within the BLA, ITC, CeL, respectively, that are proposed to be associated with fear inhibition and extinction within the amygdala ? here termed the ?Fear-Off? populations. Through a variety of cell-type specific approaches, we will determine the events underlying the inhibition of fear within three ?Fear-Off? cell types in the amygdala. Experiments will functionally and molecularly identify populations of neurons within the BLA, ITC, and CeL that participate in these processes. Our central hypothesis is that the Fear-Off pathway within the BLA-ITC-CeL circuit acts as an mPFC-regulated inhibitory gate facilitating inhibition of fear during extinction training and retention, in part through miRNA regulation of plasticity. Targeting multiple aspects of the Fear-Off pathway will expand our understanding of fear inhibition. These hypotheses will be tested through the following Specific Aims: Aim 1) mPFC Regulation of Amygdala Fear-Off Cells: To determine the differential afferent regulation from mPFC projections to BLA, ITC, and CeA ?Fear-Off? neurons through direct manipulation of afferent neurons. Aim 2) Intra-Amygdala Regulation of Fear-Off Cells: To determine the precise role of BLA, ITC, and CeA Fear-Off neurons in regulating fear output circuitry of the amygdala; and Aim 3) miRNA Regulation of Fear-Off Cells: To determine the role of miRNAs on behavior, neuronal function and plasticity within BLA, ITC, and CeA Fear-Off neurons through direct manipulation of miRNA function. We use a combinatorial approach to functionally and molecularly characterize specific target populations of amygdala neurons, which will elucidate important microcircuitry within the amygdala governing fear extinction. The identification of novel targets will advance our understanding of circuitry underlying fear behaviors and will provide unique avenues for therapeutics.